/Engine/Source/Runtime/Core/Public/HAL/FileManagerGeneric.h
Finds all the files within the given directory, with optional file extension filter.
FoundFiles, All the files that matched the optional FileExtension filter, or all files if none was specified.
virtual void FindFiles ( [TArray](API\Runtime\Core\Containers\TArray)< [FString](API\Runtime\Core\Containers\FString) > & FoundFiles, const TCHAR * Directory, const TCHAR * FileExtension )